Free piston power hammer



Jan. 19, 1937. BYFQRD 2,067,886

FREE PISTON POWER HAMMER Fil ed Sept. 13, 1935 2 Sheets-Sheet l 9 /,'I6l la E J- fiforcgbz g g fofd fli Jan. 19, 1937. H. BYFORD FREE PISTONPOWER HAMMER F iled Sept. 13, 1935 2 Sheets-Sheet 2 [lg/ENTOR ,JforqgvBy ford ry ATTORN EYS UNITED STATES Patented Jan. 19, 1937 FREE PISTONPower. 11

Application September 13, 1935, Serial No. 40,505

2 Claims.

r lE My present invention relates to the art of power hammers and moreparticularly to a free piston power hammer.

Many types of electrically driven power hammers have been created eachclaiming certain advantages. My present type of hammer is that having areciprocating piston which at the moment of impact is moving freelyalong its guiding cylinder and which is free to rebound after it hasdelivered its blow without in any way placing any shock on the mechanismdriving it. The general design of my present hammer is such that it ispossible to employ a cylindrical striking member so that an even heattreatment can be given the same, something not true of many types ofelectric hammers. Most electric hammers rely upon a plurality of rapidlydelivered light blows to accomplish their purpose. This form of energydelivery is sufiiciently effective for certain types of work, where itis necessary to deliver a heavy blow, as in riveting and demolitionwork, it is necessary to have in a single striking element enough massso that a real blow can be delivered as is required in upsetting rivetsand in shattering masonry and the like. It follows the generalprinciples that in upsetting metal a heavy hammer is used and inbreaking rock a heavy hammer is used. In both of these fields it hasbeen found that even if the same amount of energy is delivered asuccession of rapidly delivered, light blows, it is not effective. Withmy present construction I believe I have overcome the deficiency of thisgeneral class of hammers which have been offered in the past.

Another feature that has been widely sought is to provide a percussiontool of this general character which is so constructed that the shockincidental to its operation will not destroy the tool. I have providedin my present design an air cushioning arrangement similar in part tothat shown in Patent No. 1,191,948 and an improvement on said patentissued as No. 1,489,312. Each of these patents show a type of hammersimilar in certain respects to this present disclosure. It is believed,however, that in my present construction I have provided a tool whichcan be closely coupled so that it will not be unwieldy for use; whichwill use the crank shaft in the nature of a cam as distinguished fromthe type employing a connecting rod arrangement as do the patentslisted. With my present arrangement I provide for a considerablereduction in speed between the relatively high speed electric motorswhich are most efficient in this kind of work and the sleeve cylinderwhich actuates my piston striker. In this way I am able to employ arelatively heavy striker that gives the striking blow which is sonecessary in certain kinds of work.

Figure 1 is an elevation of a tool made after the teachings of myinvention, certain parts of which are broken away to better illustratethe construction.

Figure 2 is a vertical, sectional View of the form of tool shown inFigure 1, with the cutting plane revolved 90 degrees.

Figure 3 is a vertical, sectional view through a hammer of a smallersize than that shown in Figures l and 2 and showing a slightly modifiedconnection between the crank shaft and the striker piston.

Figure 4 is a fragmentary, sectional view showing the lower portion ofFigure 3 with the cutting plane revolved 90 degrees.

Referring to the drawings, throughout which like reference charactersindicate like parts, 6 designates the striker employed in my tool. This,I prefer to form as a cylindrical block of steel to the end that it maybe machined and heat treated after the best teachings of air hammerconstructions in which a relatively heavy striking piston is employed.By forming the striker as a cylinder the heat treating problem isgreatly simplified and a striker of long and useful life can beexpected. Striker ii is mounted for limited reciprocation within thestriker cylinder 8. This cylinder is preferably closed at its upper endand open at its lower end except for the collar member 9 which issecured in its lower end. This may be secured by screwing the same inplace as indicated in the drawings, or in any other suitable manner.This collar is made necessary in my present structure to assure that thepiston will be carried upwardly by cylinder 8. For certain uses it maybe desirable to insert a renewable striking face as is indicated at iii.

Cylinder 8 is in turn mounted for limited reciprocation within thesleeve housing ll. Housing II is closed at its lower end by an endclosure member ii; which in turn is provided with a tool bushing itadapted to accommodate the shank of a suitable tool at it. Cylinder 8 isreciprocated within housing M by the crank shaft 58 which issuitablyconnected to an upward extension of cylinder 8. In Figures 1 and2, which structure is intended for heavy demolition work or rockdrilling, I have shown the connecting means between the crankshaft i8and the cylinders. Extending upwardly from the top, closed end of thecylinder 3, I provide a central, rigid extension forming a cross head 8'having the rectangular opening 29. Slidabiy disposed within this openingI provide a bearing block having a rectangular exterior surface and acylindrical interior surface, and comprising two sections 2i and 22,which surround, and coact with, the crank-pin of the crankshaft 58. Itwill be apparent that the rotating motion of the crank shaft will causethe bearings 2i and 22 to reciprocate transversely of the longitudinalaxis of the cylinder along the guideway 20 thus obviating the necessityof a pivot pin or wrist pin of the cylinder. This compact arrangement ofparts provides a rugged, string and durable construction adapted forheavy-duty work.

Suitable bearings and gearings are provided to operatively connect thecrank shaft 18 with the electric motor 24. In Figures 1 and 2, in orderto get a relatively slow acting striker 6, I provided first a worm gearreduction consisting of the worm 26 secured to motor 24, the worm gear26 which, in turn, drives the pinion 30 which meshes with a gear 3|secured to crank shaft l8.

Suitable, preferably rubber faced, handles 32 and 33 are provided. Theseare secured to the motor housing at a convenient height for operationand one of the handles 33 is preferably provided with a cam member 34adapted to operatively engage the operating lever 35 of the electricalswitch 36. This serves as a convenient means for connecting motor 34with the power line 38.

In the modified form of my invention shown in Figures 3 and 4, the samestriker mechanism is employed and the piston and housing arrangement inwhich the cylinder reciprocates is very similar to the heavy type. Inthis form, however, it is permissible in the smaller forms, as shown, touse a higher striking speed. Consequently the gearing can be simplifiedand I have indicated a pinion 48 secured to the electric motor W. Thisgear is, in turn, operatively disposed in engagement with gear 44 whichis secured to crank shaft 46.

The cylinder assembly is slightly modified at its upper end. In thismodified form I find it desirable to use a built up crank shaft 46having two end members with crank webs as 4! and 48 and to secure thesame together by a stud member 59 which should be suitably keyed withinboth the web members to prevent either of the webs being angularlydisplaced with respect to the other. As in the previous forms thecylinder proper has an upward, central, transverse, extension forming anarched yoke as 5| which is machined on a radius struck from the pivotpoint 52 to form an interior bearing surface 53 and a relatively wideconnecting link 54 is provided connecting stud 50 with the pivot orwrist pin 52. Pivot 52 should be provided with ample clearance so thatthe bearing load for the retraction of the cylinder and piston willoccur or be imposed on the bearing surface 53 by head 54 thus relievingsome of the strain from the wrist pin 52. This action equalizes thetendency for wear, relieving pivot or wrist pin 52 of the retraction ofthe load which, with this tool, may be rather heavy where the striker orhammer 6 does not have a tool to rebound from. Suitable switching meansis provided at 55 so that the tool will be under easy control of theoperator at all times.

Method of operation In operating my tool, after the motor is started,the crank shaft as I8 or 46 is driven at a uniform speed in onedirection. As it is driven around each revolution of the crank shaftmoves cylinder 8 down to the lower limit of its stroke and then up toits upper limit. Assuming that the piston is at its lower limit when themotor is started; the first action is to carry up the piston or strikermember 6, which will be engaged by flange or collar 9. As soon as thecylinder 8 has reached the limit of its travel it will, of course, stopand start downwardly. The striker, however, having considerable inertiawill tend to carry on up toward the crank shaft. In so doing it will bechecked by an air cushion at the upper end of the piston and the actingas a spring not only stops the striker in its upward movement withoutjar to the mechanism, but enables it to store up within the compressedair the energy which would otherwise be wasted in destructive force onthe device itself. As soon as the striker comes to rest it will becarried down toward the tool bit i6 by cylinder 8 and the energy whichhas been stored up in the trapped air will also be added to the forceimparted to the striker by cylinder 8 and a very effective blowdelivered to the tool bit l6. Normally, as soon as the striker hits thebit there is a rebound action which starts striker 6 upwardly. Thisrebound may not carry the striker up far but it will tend to start itbackward and it will then be picked up by collar 9 with the leastpossible shock to the mechanism. Machine tolerance does not permit ofhaving too close a fit between the striker piston 6 and cylinder 8.Consequently, each time the air is trapped in the upper part of cylinder8 there is a tendency for part of the air to pass by the striker. Toprovide against any appreciable loss of air, I have provided the smallspring loaded valves 59 and 59 which open on the downward stroke. Aresupply of air is provided. by ports 50 which are, in turn, providedwith elongated opening 62 to the end that air will be supplied to thecrank case proper through a considerable portion of the stroke of thecylinder to the end that sumping will not be affected; it normally beingarranged that the piston covers the ports during the major portion ofits movement.

The foregoing description and the accompanying drawings are believed toclearly disclose a preferred embodiment of my invention, but it will beunderstood that this disclosure is merely illustrative and that suchchanges in the invention may be made as are fairly within the scope andspirit of the following claims:

Having thus fully described my invention, what I claim as new and desireto secure by Letters Patent is:

1. In a power operated hammer, the combination with a barrel having acrank shaft journaled therein, a cylinder in said barrel having a valveseat in its upper end, an inwardly opening spring pressed air valve insaid seat, a freestriking piston in said cylinder, a spring interposedbetween the piston and the upper end of I I the cylinder, a cross headon the cylinder, and means forming a transversely reciprocating bearingbetween said cross head and said crank shaft.

2. In a power operated hammer, the combination with a barrel having acrank shaft journaled therein, a cylinder in said barrel having a valveseat in its upper end and an inwardly opening spring-pressed valve insaid seat, an annular collar threaded in the lower end of the cylinder,a free striking piston in said cylinder, a slotted cross head on theexterior of the cylinder, a rectangular bearing block reciprocabletransversely in said slot, and a spring interposed between the pistonand the cylinder.

HORACE BYFORD.

